 Hello. Myself Sunil Kalshatti, Assistant Professor, Department of Electronics Engineering, Walchin Institute of Technology, Sulapur. Today, I am going to explain the power IGBT from Industrial Electronics Learning.com. At the end of this session, students can describe the construction, working and characteristics of power IGBT. Insulated gate bipolar transistor, it is the another development in the power MOS technology is the IGBT. This device combines the best qualities of power MOSFET and power BJT. As we know, MOSFET is the voltage control device for the MOSFET input impedance is very high and power BJT, power BJT is the current control device, input impedance is low, but on set drop is less. These two features are utilized here. It is the combination of BJT and MOSFET. It has high input impedance like MOSFET and low on set conduction losses like BJT. It is the free from second breakdown problem present in the BJT. As we know, BJT is the NTC, that is why there is a possibility of second breakdown. But IGBT is the PTC, so as the temperature encourages, resistance encourages, current reduces, so there is no possibility of second breakdown problem. IGBT is the voltage control device and IGBT is basically hybrid MOS, gated turn on of bipolar transistor that combines the attributes of MOSFET, BJT and thyristor. It is the latch-proof device, means as long as input is present, the device remains in conducting state. Once we remove the input, the device turns off, that is why IGBT is called as a latch-proof device. IGBTs are available up to 1500 volt and 1000 ampere, basically IGBTs are used in the high power application. The switching frequency of IGBT is up to 30 kilohertz, turn on time is less than 1 microsecond and turn off time is nearly equal to 0.1 microsecond. Other name of device, insulated gate transistor, IGBT, COMFET, conductivity modulated field effect transistor. It is also called as a gemFET, gain enhanced metal oxide semiconductor field effect transistor and bipolar MOS transistor, these are other name of the devices. It is a schematic symbol of the IGBT, it has three terminals, emitter, gate and collector. Here the input characteristics is similar to MOSFET and output characteristics is similar to BJT. It is the basic structure of IGBT, IGBT hang the different layers. The first bottom layer is the P plus region, it is the injecting layer. Second layer is the N plus buffer layer. These two layer forms the junction Z1. The third layer is the N minus layer, the doping density is slightly less than buffer layer. So this layer is called as a drain drift layer. Fourth one is the body region, P region is the body region and last one is the N plus region. The body region and N plus region forms the junction Z3, whereas the drain drift region and the body region forms the junction Z2, means it consists of the three junctions. The cross section of the IGBT is identical to the MOSFET except the P plus region. The IGBT is just the interdigited gate source structure in order to reduce the possibility of current corroding. The doping layer is used in the different layer of IGBT as similar to MOSFET structure except the P plus layer. Why? Performance of IGBT is closer to BJT than MOSFET. The construction of IGBT is similar to MOSFET except the P plus region. The bottom layer is the P plus region. This layer is responsible for injecting the charge carriers. So effect of this, the current flows through because of holes and electrons. That's why the performance of IGBT is closer to BJT, it is the construction of IGBT. The bottom layer P plus region, the middle one is the drain drift region, N region and the body region, it forms the parasitic PNP transistor and whereas the upper one N plus region, body region and the drain drift region forms the parasitic NPN transistor. The combination of these two transistors forms the parasitic thyristor and the MOSFET is shown by the dotted lines. IGBT cell has the parasitic N channel MOSFET structure embedded in it is as shown in figure. The important resistance in the current flow path are also indicated. It is the exact equivalent circuit of IGBT cell structure. When we apply the voltage across the collector with respect to emitter, the current flows through the collector to emitter. So because of this, the parasitic thyristor gets latched into the conducting state and the gate loses the control over the device. That's why it is essential to avoid the latching and how latch up is avoided in the IGBT. To overcome the latching problem, the parasitic NPN transistor is prevented by controlling the the resistivity of the P region means body region and short the P and N plus region by the emitter terminal. So the latching is avoided. So after shorting the P and N plus region, the the equivalent circuit becomes like this. IGBT VI characteristics it shows the a relation between the collector voltage with respect to collector current IGBT VI characteristics. For this mode, the VG is less than thyristor voltage and apply the voltage in between the collector with respect to emitter junction J2 is reverse bias and at the same time junction J1, J3 are forward bias. No channel will be induced in the P region so device operates in the forward blocking mode. For this mode, the VG is less than thyristor voltage channel will absent so collector current is 0. For this mode, the VGE greater than VT and apply the collector voltage with respect to emitter. As long as VGE is less than VT channel will absent so collector current remains 0. Now increase the VGE gate is at positive potential so the electrons from the body region are attracted towards the gate potential but they cannot reach up to the gate terminal because in between gate and body there is the thin layer of oxide layer. So the electrons are accumulated near the surface of oxide layer. So as the VGE encourages when the VGE crosses the VT at that instant the channel will formed means the sufficient number of electrons are deposited in the P region. So effect of this the P region loses its identity as a P region and behaves as a N region and channel will formed and the electrons are starts flowing from the emitter to collector. So effect of this current starts flowing from the collector to emitter. The voltage at which the channel will formed that voltage is called as a thyristor voltage as long as VGE is less than VT device remains in off state. When the VGE crosses the thyristor voltage the P region loses its identity as a P region and behaves as a N region and the device forms as a pin diode it behaves as a pin diode so pin diode. High resistivity intrinsic layer is sandwiched in between the P and N region this high resistance of intrinsic layer produce the large electric field and the electron hole pair generation is enhanced. IGBT transfer characteristics shows the relation between the gate voltage and collector current as long as gate voltage is less than thyristor voltage the collector current is nearly equal to 0. Once the VGE crosses the thyristor voltage the collector current encourages and device enters in the conduction state these are the references thank you.